License

I explored different options for realtime audio input (see below for a summary) before having to settling for this option. Unfortunately this solution requires Windows and the Data Acquisition toolbox. I hope to be able to report at some point that this function has been superceded by something more generally useful, so please let me know if you come across something better.

Other possibilities:
PortAudio (http://www.portaudio.com/): seem to be the workhorse of audio input, but it's in C++, not Matlab code

PlayRec.m (http://www.playrec.co.uk/): An adaptation of PortAudio for Matlab. However, support seems to have ended around 2008, and I know several people who have spent many hours failing to compile it for more recent operating systems and/or Matlab versions.

PsychPortAudio (http://docs.psychtoolbox.org/PsychPortAudio): This may be the best option, although it requires PsychToolbox, which can be challenging to install itself. Can anyone confirm that PsychPortAudio works for realtime audio input?

In the meantime, the detailed function of tgrabaudio.m is described in its help section, copied below for convenience:

fs = the sample-rate [default = 44100]
maxduration = the maximum delay (in seconds) that is considered an
acceptable build-up of audio samples. If this buffer is
exceeded during auditory capture, an error will be generated.

This clears the persistent variables and stops the background audio
input. Careful, if this step is omitted, Matlab is likely to crash or
behave strangely the next time tgrabaudio is run. NB if a program that
uses tgrabaudio crashes before calling tgrabaudio('stop'), don't forget
to call tgrabaudio('stop') as soon as possible (either manually or using
Matlab's try...catch keywords).

EXAMPLE:

The following code shows how to use tgrabaudio to input sound in
realtime. For demo purposes, the audio is gathered over a finite period,
reconstructed into a single variable, and then simply played back.
However, the same construction could be used for continuous processing of
audio input.

You may be able to adapt it to work with that specific microphone. If you do, I would perhaps check that it is able to process the sound fast enough, otherwise you might get glitches. You could test it by recording (for example) a pure tone, for which glitches might be more obvious.

I need to use the inbuilt microphone of my laptop to get a signal which has to then be A-weighted to calculate the db(A)-SPL value of the sound.
My short-time goal is to take real-time input from the microphone, filter it by a-weighting and generate a noise map of the sounds in a classroom environment.